We're quibbling at definitions. Would regulatory burden be better?"Overhead" is a term used to refer to the ongoing expenses of operating a business.
It wouldnt apply to a nonlicensee and most certiainly is the smallest expense of any FFL.
And since this thread is about online vs local gun stores that pretty much makes the context about BUSINESS expenses.
The OP used books as examples of online sales damaging local retail. The difference being that you can have most any product shipped to your door except a gun. To buy a gun you have to walk into a gun store. It may not be where you paid for it but it the only place you can walk out with it. Firearms are a rare retail case there.
Back to my initial response I see the trend leading tward more places doing used trading and transfers without stocking much in the way of new production stuff. That wont apply to everywhere but I see it as more common than a large stock of new production stuff. Easier and safer to order in what a customer wants from your distributor.